Hi Guys,
The Pin-SMX completely isolates the inputs from each other. We used small isolation transformers so there wouldn't be any interaction between games. You can now mix up to 4 games into one subwoofer. Each of the four input levels can be adjusted and balanced too! We just received the prototype boards in yesterday and built our first demo. I tested it out on my STNG and it works great!
Pin-SMX is compatible with our mute button on our Stern Sam headphone kits. When you mute the system speakers, it also mutes that machines audio in the subwoofer.

Thanks,
Mark

Adding Diodes in the path of an audio signal will probably cause distortion.
The diode would rectify the audio...only half of the audio would make it through the diode. A typical diode has a 0.7 V droop across it. If the audio level was less than 0.7V, nothing would make it past the diode.

I tried a few methods for mixing the audio while developing Pin-SMX. Using resistors to mix the audio almost worked but I needed to keep the grounds isolated so our headphone kit would mute properly. The final solution was to use a small isolation transformer to get the job done. The transformers add cost but it keeps everything completely isolated! Aka: No Ground loops!

One more thing.. This is a completely passive mixer. It does not need any power supply to make it work.